(1) Field of the Invention
The invention relates to an electric power switching device, monopolar or multipolar, of relay, contactor or contactor breaker type, whose closing and opening movements between moving contacts and stationary contacts are carried out via an approach actuator and a force actuator. The invention also relates to a closing and opening method of the contacts of such a switching device.
(2) Description of the Related Art
An electric switching device of relay type, contactor or contactor breaker is a device usually employed to perform the electric switching or commutation of a power charge, for example a motor. For this, it usually has, for each power pole, a movable bridge driven by an actuator generally constituted of an electromagnet common to the different poles and equipped with restoring means such as a return spring. The movable bridge has a single switching movable contact, or two double switching movable contacts, co-operating with one, respectively two, fixed contact(s), so as to break or make the flow of electric current in the power poles. Moreover, to obtain sufficient contact pressure, we usually employ pressure contact springs acting on the movable contacts.
The actuator can be controlled via a manual command by an operator or via a command sent by an automatic control. The moment that these commands appear is of course then out of sync with the intensity of current flowing in the different power poles of the switching device at this moment. Therefore, at the time of the opening movement corresponding to the separating of the fixed and movable contacts, a significant electric current could be circulating in the poles thus creating, in a continuous manner, an electric switching arc between the fixed and movable contacts. This switching arc requires an arc extinguishing chamber in the device and eventually accelerates the wear of the contact tips deposited on the fixed and movable contacts. To limit this inconvenience, the electromagnet has usually restoring means, such as a return spring, sufficiently significant to have the quickest possible separation between the fixed and movable contacts. However, at the time of the reverse closing movement corresponding to the bringing together of the fixed and movable contacts, this return force must be overcome which requires the increasing in size and strength of this electromagnet.